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 $59.28   11.668%   $66.1968   $66.20   $66.20   $66.20  
  Purchase #2 $148.71   9.510%   $162.8523   $162.85   $162.85   $162.90  
  Purchase #3 $240.98   4.332%   $251.4193   $251.42   $251.40   $251.40  
  Purchase #4 $181.68   10.810%   $201.3196   $201.32   $201.30   $201.30  
  Purchase #5 $104.53   3.320%   $108.0004   $108.00   $108.00   $108.00  
  Purchase #6 $229.25   4.209%   $238.8991   $238.90   $238.90   $238.90  
  Purchase #7 $152.91   12.551%   $172.1017   $172.10   $172.10   $172.10  
  7 purchase totals = $1,117.34       $1,200.7892   $1,200.79   $1,200.75   $1,200.80