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 $39.74   9.164%   $43.3818   $43.38   $43.40   $43.40  
  Purchase #2 $181.25   13.396%   $205.5303   $205.53   $205.55   $205.50  
  Purchase #3 $248.48   4.861%   $260.5586   $260.56   $260.55   $260.60  
  Purchase #4 $169.30   5.484%   $178.5844   $178.58   $178.60   $178.60  
  Purchase #5 $63.83   10.717%   $70.6707   $70.67   $70.65   $70.70  
  Purchase #6 $143.52   6.859%   $153.364   $153.36   $153.35   $153.40  
  Purchase #7 $27.37   13.368%   $31.0288   $31.03   $31.05   $31.00  
  7 purchase totals = $873.49       $943.1186   $943.11   $943.15   $943.20