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 $127.52   13.508%   $144.7454   $144.75   $144.75   $144.70  
  Purchase #2 $220.84   4.313%   $230.3648   $230.36   $230.35   $230.40  
  Purchase #3 $54.82   4.166%   $57.1038   $57.10   $57.10   $57.10  
  Purchase #4 $63.67   8.459%   $69.0558   $69.06   $69.05   $69.10  
  Purchase #5 $214.77   9.840%   $235.9034   $235.90   $235.90   $235.90  
  Purchase #6 $139.79   6.533%   $148.9225   $148.92   $148.90   $148.90  
  Purchase #7 $228.73   12.708%   $257.797   $257.80   $257.80   $257.80  
  7 purchase totals = $1,050.14       $1,143.8927   $1,143.89   $1,143.85   $1,143.90