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 $71.39   5.782%   $75.5178   $75.52   $75.50   $75.50  
  Purchase #2 $114.85   3.707%   $119.1075   $119.11   $119.10   $119.10  
  Purchase #3 $190.36   5.594%   $201.0087   $201.01   $201.00   $201.00  
  Purchase #4 $152.50   9.141%   $166.44   $166.44   $166.45   $166.40  
  Purchase #5 $18.81   6.390%   $20.012   $20.01   $20.00   $20.00  
  Purchase #6 $244.67   9.678%   $268.3492   $268.35   $268.35   $268.30  
  Purchase #7 $161.57   9.467%   $176.8658   $176.87   $176.85   $176.90  
  7 purchase totals = $954.15       $1,027.3010   $1,027.31   $1,027.25   $1,027.20