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 $131.79   8.726%   $143.29   $143.29   $143.30   $143.30  
  Purchase #2 $67.27   3.837%   $69.8511   $69.85   $69.85   $69.90  
  Purchase #3 $10.85   7.201%   $11.6313   $11.63   $11.65   $11.60  
  Purchase #4 $54.49   7.250%   $58.4405   $58.44   $58.45   $58.40  
  Purchase #5 $162.30   7.219%   $174.0164   $174.02   $174.00   $174.00  
  Purchase #6 $71.25   5.782%   $75.3697   $75.37   $75.35   $75.40  
  Purchase #7 $165.54   4.231%   $172.544   $172.54   $172.55   $172.50  
  7 purchase totals = $663.49       $705.1430   $705.14   $705.15   $705.10