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 $60.46   8.753%   $65.7521   $65.75   $65.75   $65.80  
  Purchase #2 $52.81   13.375%   $59.8733   $59.87   $59.85   $59.90  
  Purchase #3 $6.94   8.387%   $7.5221   $7.52   $7.50   $7.50  
  Purchase #4 $8.93   4.672%   $9.3472   $9.35   $9.35   $9.30  
  Purchase #5 $165.26   3.676%   $171.335   $171.34   $171.35   $171.30  
  Purchase #6 $123.31   4.206%   $128.4964   $128.50   $128.50   $128.50  
  Purchase #7 $148.68   4.549%   $155.4435   $155.44   $155.45   $155.40  
  7 purchase totals = $566.39       $597.7696   $597.77   $597.75   $597.70