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 $246.59   8.517%   $267.5921   $267.59   $267.60   $267.60  
  Purchase #2 $190.34   7.364%   $204.3566   $204.36   $204.35   $204.40  
  Purchase #3 $220.64   6.610%   $235.2243   $235.22   $235.20   $235.20  
  Purchase #4 $49.30   12.581%   $55.5024   $55.50   $55.50   $55.50  
  Purchase #5 $179.47   12.441%   $201.7979   $201.80   $201.80   $201.80  
  Purchase #6 $123.31   11.629%   $137.6497   $137.65   $137.65   $137.60  
  Purchase #7 $185.45   7.514%   $199.3847   $199.38   $199.40   $199.40  
  7 purchase totals = $1,195.10       $1,301.5077   $1,301.50   $1,301.50   $1,301.50