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 $238.31   11.336%   $265.3248   $265.32   $265.30   $265.30  
  Purchase #2 $202.55   12.533%   $227.9356   $227.94   $227.95   $227.90  
  Purchase #3 $40.85   7.803%   $44.0375   $44.04   $44.05   $44.00  
  Purchase #4 $148.74   5.400%   $156.772   $156.77   $156.75   $156.80  
  Purchase #5 $83.50   5.751%   $88.3021   $88.30   $88.30   $88.30  
  Purchase #6 $42.80   9.797%   $46.9931   $46.99   $47.00   $47.00  
  Purchase #7 $208.26   5.137%   $218.9583   $218.96   $218.95   $219.00  
  7 purchase totals = $965.01       $1,048.3234   $1,048.32   $1,048.30   $1,048.30