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 $56.36   9.646%   $61.7965   $61.80   $61.80   $61.80  
  Purchase #2 $147.84   13.585%   $167.9241   $167.92   $167.90   $167.90  
  Purchase #3 $64.40   6.125%   $68.3445   $68.34   $68.35   $68.30  
  Purchase #4 $53.31   3.633%   $55.2468   $55.25   $55.25   $55.20  
  Purchase #5 $230.54   6.559%   $245.6611   $245.66   $245.65   $245.70  
  Purchase #6 $246.84   4.198%   $257.2023   $257.20   $257.20   $257.20  
  Purchase #7 $28.93   10.634%   $32.0064   $32.01   $32.00   $32.00  
  7 purchase totals = $828.22       $888.1817   $888.18   $888.15   $888.10