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 $57.64   6.839%   $61.582   $61.58   $61.60   $61.60  
  Purchase #2 $200.47   11.776%   $224.0773   $224.08   $224.10   $224.10  
  Purchase #3 $133.89   11.861%   $149.7707   $149.77   $149.75   $149.80  
  Purchase #4 $56.37   12.245%   $63.2725   $63.27   $63.25   $63.30  
  Purchase #5 $202.55   11.534%   $225.9121   $225.91   $225.90   $225.90  
  Purchase #6 $150.42   6.837%   $160.7042   $160.70   $160.70   $160.70  
  Purchase #7 $29.27   8.468%   $31.7486   $31.75   $31.75   $31.70  
  7 purchase totals = $830.61       $917.0674   $917.06   $917.05   $917.10