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 $66.65   13.687%   $75.7724   $75.77   $75.75   $75.80  
  Purchase #2 $77.86   5.319%   $82.0014   $82.00   $82.00   $82.00  
  Purchase #3 $189.54   12.268%   $212.7928   $212.79   $212.80   $212.80  
  Purchase #4 $128.94   6.306%   $137.071   $137.07   $137.05   $137.10  
  Purchase #5 $232.30   13.577%   $263.8394   $263.84   $263.85   $263.80  
  Purchase #6 $77.92   7.425%   $83.7056   $83.71   $83.70   $83.70  
  Purchase #7 $225.35   11.249%   $250.6996   $250.70   $250.70   $250.70  
  7 purchase totals = $998.56       $1,105.8822   $1,105.88   $1,105.85   $1,105.90