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 $135.82   8.854%   $147.8455   $147.85   $147.85   $147.80  
  Purchase #2 $212.95   10.662%   $235.6547   $235.65   $235.65   $235.70  
  Purchase #3 $155.27   8.831%   $168.9819   $168.98   $169.00   $169.00  
  Purchase #4 $203.67   6.778%   $217.4748   $217.47   $217.45   $217.50  
  Purchase #5 $125.76   12.148%   $141.0373   $141.04   $141.05   $141.00  
  Purchase #6 $124.26   8.108%   $134.335   $134.34   $134.35   $134.30  
  Purchase #7 $76.54   13.342%   $86.752   $86.75   $86.75   $86.80  
  7 purchase totals = $1,034.27       $1,132.0812   $1,132.08   $1,132.10   $1,132.10