Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $188.99   11.280%   $210.3081   $210.31   $210.30   $210.30  
  Purchase #2 $119.66   13.281%   $135.552   $135.55   $135.55   $135.60  
  Purchase #3 $162.74   4.256%   $169.6662   $169.67   $169.65   $169.70  
  Purchase #4 $149.41   11.824%   $167.0762   $167.08   $167.10   $167.10  
  Purchase #5 $123.70   10.170%   $136.2803   $136.28   $136.30   $136.30  
  Purchase #6 $193.55   5.385%   $203.9727   $203.97   $203.95   $204.00  
  Purchase #7 $67.53   11.776%   $75.4823   $75.48   $75.50   $75.50  
  7 purchase totals = $1,005.58       $1,098.3378   $1,098.34   $1,098.35   $1,098.50