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 $86.70   10.631%   $95.9171   $95.92   $95.90   $95.90  
  Purchase #2 $69.31   9.138%   $75.6435   $75.64   $75.65   $75.60  
  Purchase #3 $67.81   12.677%   $76.4063   $76.41   $76.40   $76.40  
  Purchase #4 $28.45   10.258%   $31.3684   $31.37   $31.35   $31.40  
  Purchase #5 $43.67   11.852%   $48.8458   $48.85   $48.85   $48.80  
  Purchase #6 $20.93   7.817%   $22.5661   $22.57   $22.55   $22.60  
  Purchase #7 $141.73   6.776%   $151.3336   $151.33   $151.35   $151.30  
  7 purchase totals = $458.60       $502.0808   $502.09   $502.05   $502.00