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 $213.56   12.429%   $240.1034   $240.10   $240.10   $240.10  
  Purchase #2 $66.68   11.775%   $74.5316   $74.53   $74.55   $74.50  
  Purchase #3 $82.94   9.170%   $90.5456   $90.55   $90.55   $90.50  
  Purchase #4 $158.95   4.850%   $166.6591   $166.66   $166.65   $166.70  
  Purchase #5 $230.67   6.339%   $245.2922   $245.29   $245.30   $245.30  
  Purchase #6 $102.42   13.855%   $116.6103   $116.61   $116.60   $116.60  
  Purchase #7 $76.35   5.374%   $80.453   $80.45   $80.45   $80.50  
  7 purchase totals = $931.57       $1,014.1952   $1,014.19   $1,014.20   $1,014.20