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 $91.39   11.588%   $101.9803   $101.98   $102.00   $102.00  
  Purchase #2 $234.66   4.388%   $244.9569   $244.96   $244.95   $245.00  
  Purchase #3 $149.87   3.110%   $154.531   $154.53   $154.55   $154.50  
  Purchase #4 $248.74   9.472%   $272.3007   $272.30   $272.30   $272.30  
  Purchase #5 $178.85   12.507%   $201.2188   $201.22   $201.20   $201.20  
  Purchase #6 $144.56   9.436%   $158.2007   $158.20   $158.20   $158.20  
  Purchase #7 $228.79   5.412%   $241.1721   $241.17   $241.15   $241.20  
  7 purchase totals = $1,276.86       $1,374.3605   $1,374.36   $1,374.35   $1,374.40