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 $55.98   10.319%   $61.7566   $61.76   $61.75   $61.80  
  Purchase #2 $31.52   10.869%   $34.9459   $34.95   $34.95   $34.90  
  Purchase #3 $20.89   8.588%   $22.684   $22.68   $22.70   $22.70  
  Purchase #4 $118.79   10.480%   $131.2392   $131.24   $131.25   $131.20  
  Purchase #5 $241.26   9.459%   $264.0808   $264.08   $264.10   $264.10  
  Purchase #6 $200.60   8.146%   $216.9409   $216.94   $216.95   $216.90  
  Purchase #7 $72.31   9.221%   $78.9777   $78.98   $79.00   $79.00  
  7 purchase totals = $741.35       $810.6251   $810.63   $810.70   $810.60