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 $59.93   9.467%   $65.6036   $65.60   $65.60   $65.60  
  Purchase #2 $159.39   6.386%   $169.5686   $169.57   $169.55   $169.60  
  Purchase #3 $119.64   12.845%   $135.0078   $135.01   $135.00   $135.00  
  Purchase #4 $206.60   9.232%   $225.6733   $225.67   $225.65   $225.70  
  Purchase #5 $210.58   10.517%   $232.7267   $232.73   $232.75   $232.70  
  Purchase #6 $178.51   10.206%   $196.7287   $196.73   $196.75   $196.70  
  Purchase #7 $63.85   7.849%   $68.8616   $68.86   $68.85   $68.90  
  7 purchase totals = $998.50       $1,094.1703   $1,094.17   $1,094.15   $1,094.20