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 $48.66   10.199%   $53.6228   $53.62   $53.60   $53.60  
  Purchase #2 $77.32   12.498%   $86.9835   $86.98   $87.00   $87.00  
  Purchase #3 $36.39   8.427%   $39.4566   $39.46   $39.45   $39.50  
  Purchase #4 $131.71   8.294%   $142.634   $142.63   $142.65   $142.60  
  Purchase #5 $236.50   10.164%   $260.5379   $260.54   $260.55   $260.50  
  Purchase #6 $147.86   10.585%   $163.511   $163.51   $163.50   $163.50  
  Purchase #7 $160.37   12.142%   $179.8421   $179.84   $179.85   $179.80  
  7 purchase totals = $838.81       $926.5879   $926.58   $926.60   $926.50