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 $53.45   13.485%   $60.6577   $60.66   $60.65   $60.70  
  Purchase #2 $99.40   5.563%   $104.9296   $104.93   $104.95   $104.90  
  Purchase #3 $154.34   3.874%   $160.3191   $160.32   $160.30   $160.30  
  Purchase #4 $229.50   3.821%   $238.2692   $238.27   $238.25   $238.30  
  Purchase #5 $19.61   13.689%   $22.2944   $22.29   $22.30   $22.30  
  Purchase #6 $170.65   5.186%   $179.4999   $179.50   $179.50   $179.50  
  Purchase #7 $246.35   9.340%   $269.3591   $269.36   $269.35   $269.40  
  7 purchase totals = $973.30       $1,035.3290   $1,035.33   $1,035.30   $1,035.40