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 $33.41   12.765%   $37.6748   $37.67   $37.65   $37.70  
  Purchase #2 $166.57   4.809%   $174.5804   $174.58   $174.60   $174.60  
  Purchase #3 $37.36   9.271%   $40.8236   $40.82   $40.80   $40.80  
  Purchase #4 $201.28   4.693%   $210.7261   $210.73   $210.75   $210.70  
  Purchase #5 $212.58   7.227%   $227.9432   $227.94   $227.95   $227.90  
  Purchase #6 $120.82   3.164%   $124.6427   $124.64   $124.65   $124.60  
  Purchase #7 $63.97   7.763%   $68.936   $68.94   $68.95   $68.90  
  7 purchase totals = $835.99       $885.3268   $885.32   $885.35   $885.20