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 $30.35   6.382%   $32.2869   $32.29   $32.30   $32.30  
  Purchase #2 $181.93   12.654%   $204.9514   $204.95   $204.95   $205.00  
  Purchase #3 $152.84   9.765%   $167.7648   $167.76   $167.75   $167.80  
  Purchase #4 $232.73   5.479%   $245.4813   $245.48   $245.50   $245.50  
  Purchase #5 $249.48   6.595%   $265.9332   $265.93   $265.95   $265.90  
  Purchase #6 $133.75   11.754%   $149.471   $149.47   $149.45   $149.50  
  Purchase #7 $122.57   7.363%   $131.5948   $131.59   $131.60   $131.60  
  7 purchase totals = $1,103.65       $1,197.4834   $1,197.47   $1,197.50   $1,197.60