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 $99.99   10.500%   $110.489   $110.49   $110.50   $110.50  
  Purchase #2 $161.72   12.142%   $181.356   $181.36   $181.35   $181.40  
  Purchase #3 $45.83   8.732%   $49.8319   $49.83   $49.85   $49.80  
  Purchase #4 $180.41   8.411%   $195.5843   $195.58   $195.60   $195.60  
  Purchase #5 $20.47   10.362%   $22.5911   $22.59   $22.60   $22.60  
  Purchase #6 $194.29   8.123%   $210.0722   $210.07   $210.05   $210.10  
  Purchase #7 $55.70   11.326%   $62.0086   $62.01   $62.00   $62.00  
  7 purchase totals = $758.41       $831.9331   $831.93   $831.95   $832.00