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 $59.40   7.830%   $64.051   $64.05   $64.05   $64.10  
  Purchase #2 $29.95   5.668%   $31.6476   $31.65   $31.65   $31.60  
  Purchase #3 $45.53   11.262%   $50.6576   $50.66   $50.65   $50.70  
  Purchase #4 $65.96   7.546%   $70.9373   $70.94   $70.95   $70.90  
  Purchase #5 $81.34   5.623%   $85.9137   $85.91   $85.90   $85.90  
  Purchase #6 $177.96   5.404%   $187.577   $187.58   $187.60   $187.60  
  Purchase #7 $114.43   13.775%   $130.1927   $130.19   $130.20   $130.20  
  7 purchase totals = $574.57       $620.9769   $620.98   $621.00   $621.00