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 $91.91   7.456%   $98.7628   $98.76   $98.75   $98.80  
  Purchase #2 $226.52   11.839%   $253.3377   $253.34   $253.35   $253.30  
  Purchase #3 $73.52   8.844%   $80.0221   $80.02   $80.00   $80.00  
  Purchase #4 $96.53   6.217%   $102.5313   $102.53   $102.55   $102.50  
  Purchase #5 $33.50   3.109%   $34.5415   $34.54   $34.55   $34.50  
  Purchase #6 $53.48   9.597%   $58.6125   $58.61   $58.60   $58.60  
  Purchase #7 $247.56   10.809%   $274.3188   $274.32   $274.30   $274.30  
  7 purchase totals = $823.02       $902.1267   $902.12   $902.10   $902.00