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 $194.69   5.338%   $205.0826   $205.08   $205.10   $205.10  
  Purchase #2 $229.38   8.467%   $248.8016   $248.80   $248.80   $248.80  
  Purchase #3 $250.31   6.502%   $266.5852   $266.59   $266.60   $266.60  
  Purchase #4 $26.53   5.261%   $27.9257   $27.93   $27.95   $27.90  
  Purchase #5 $58.27   3.868%   $60.5239   $60.52   $60.50   $60.50  
  Purchase #6 $138.79   3.444%   $143.5699   $143.57   $143.55   $143.60  
  Purchase #7 $78.58   8.304%   $85.1053   $85.11   $85.10   $85.10  
  7 purchase totals = $976.55       $1,037.5942   $1,037.60   $1,037.60   $1,037.60