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 $66.72   6.598%   $71.1222   $71.12   $71.10   $71.10  
  Purchase #2 $140.44   5.860%   $148.6698   $148.67   $148.65   $148.70  
  Purchase #3 $153.54   10.584%   $169.7907   $169.79   $169.80   $169.80  
  Purchase #4 $202.36   4.662%   $211.794   $211.79   $211.80   $211.80  
  Purchase #5 $18.77   4.341%   $19.5848   $19.58   $19.60   $19.60  
  Purchase #6 $168.89   13.118%   $191.045   $191.05   $191.05   $191.00  
  Purchase #7 $219.49   12.515%   $246.9592   $246.96   $246.95   $247.00  
  7 purchase totals = $970.21       $1,058.9657   $1,058.96   $1,058.95   $1,059.00