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 $233.53   8.363%   $253.0601   $253.06   $253.05   $253.10  
  Purchase #2 $169.31   8.680%   $184.0061   $184.01   $184.00   $184.00  
  Purchase #3 $71.26   11.602%   $79.5276   $79.53   $79.55   $79.50  
  Purchase #4 $182.84   11.483%   $203.8355   $203.84   $203.85   $203.80  
  Purchase #5 $231.66   6.654%   $247.0747   $247.07   $247.05   $247.10  
  Purchase #6 $59.42   5.759%   $62.842   $62.84   $62.85   $62.80  
  Purchase #7 $193.33   9.310%   $211.329   $211.33   $211.35   $211.30  
  7 purchase totals = $1,141.35       $1,241.6750   $1,241.68   $1,241.70   $1,241.60