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 $97.41   11.677%   $108.7846   $108.78   $108.80   $108.80  
  Purchase #2 $73.58   6.227%   $78.1618   $78.16   $78.15   $78.20  
  Purchase #3 $248.32   6.456%   $264.3515   $264.35   $264.35   $264.40  
  Purchase #4 $181.27   11.812%   $202.6816   $202.68   $202.70   $202.70  
  Purchase #5 $123.44   12.799%   $139.2391   $139.24   $139.25   $139.20  
  Purchase #6 $167.30   11.183%   $186.0092   $186.01   $186.00   $186.00  
  Purchase #7 $70.40   6.159%   $74.7359   $74.74   $74.75   $74.70  
  7 purchase totals = $961.72       $1,053.9637   $1,053.96   $1,054.00   $1,054.00