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 $82.75   6.293%   $87.9575   $87.96   $87.95   $88.00  
  Purchase #2 $72.96   12.336%   $81.9603   $81.96   $81.95   $82.00  
  Purchase #3 $226.49   13.412%   $256.8668   $256.87   $256.85   $256.90  
  Purchase #4 $134.93   10.471%   $149.0585   $149.06   $149.05   $149.10  
  Purchase #5 $123.60   11.274%   $137.5347   $137.53   $137.55   $137.50  
  Purchase #6 $194.48   5.593%   $205.3573   $205.36   $205.35   $205.40  
  Purchase #7 $142.83   8.550%   $155.042   $155.04   $155.05   $155.00  
  7 purchase totals = $978.04       $1,073.7771   $1,073.78   $1,073.75   $1,073.90