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 $232.61   11.360%   $259.0345   $259.03   $259.05   $259.00  
  Purchase #2 $125.56   7.753%   $135.2947   $135.29   $135.30   $135.30  
  Purchase #3 $67.76   7.485%   $72.8318   $72.83   $72.85   $72.80  
  Purchase #4 $60.81   13.665%   $69.1197   $69.12   $69.10   $69.10  
  Purchase #5 $138.96   8.309%   $150.5062   $150.51   $150.50   $150.50  
  Purchase #6 $189.27   7.741%   $203.9214   $203.92   $203.90   $203.90  
  Purchase #7 $121.99   3.623%   $126.4097   $126.41   $126.40   $126.40  
  7 purchase totals = $936.96       $1,017.1180   $1,017.11   $1,017.10   $1,017.00