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 $182.72   11.294%   $203.3564   $203.36   $203.35   $203.40  
  Purchase #2 $69.25   9.744%   $75.9977   $76.00   $76.00   $76.00  
  Purchase #3 $155.57   10.478%   $171.8706   $171.87   $171.85   $171.90  
  Purchase #4 $222.54   9.624%   $243.9572   $243.96   $243.95   $244.00  
  Purchase #5 $144.59   7.399%   $155.2882   $155.29   $155.30   $155.30  
  Purchase #6 $237.71   7.201%   $254.8275   $254.83   $254.85   $254.80  
  Purchase #7 $143.67   6.359%   $152.806   $152.81   $152.80   $152.80  
  7 purchase totals = $1,156.05       $1,258.1036   $1,258.12   $1,258.10   $1,258.20