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 $117.96   12.422%   $132.613   $132.61   $132.60   $132.60  
  Purchase #2 $65.28   8.354%   $70.7335   $70.73   $70.75   $70.70  
  Purchase #3 $180.84   11.160%   $201.0217   $201.02   $201.00   $201.00  
  Purchase #4 $85.91   8.102%   $92.8704   $92.87   $92.85   $92.90  
  Purchase #5 $42.79   4.272%   $44.618   $44.62   $44.60   $44.60  
  Purchase #6 $201.98   11.841%   $225.8965   $225.90   $225.90   $225.90  
  Purchase #7 $171.99   8.330%   $186.3168   $186.32   $186.30   $186.30  
  7 purchase totals = $866.75       $954.0699   $954.07   $954.00   $954.00