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 $53.96   4.775%   $56.5366   $56.54   $56.55   $56.50  
  Purchase #2 $140.67   3.504%   $145.5991   $145.60   $145.60   $145.60  
  Purchase #3 $112.84   13.240%   $127.78   $127.78   $127.80   $127.80  
  Purchase #4 $24.79   12.220%   $27.8193   $27.82   $27.80   $27.80  
  Purchase #5 $23.86   11.746%   $26.6626   $26.66   $26.65   $26.70  
  Purchase #6 $34.80   11.523%   $38.81   $38.81   $38.80   $38.80  
  Purchase #7 $225.68   6.779%   $240.9788   $240.98   $241.00   $241.00  
  7 purchase totals = $616.60       $664.1864   $664.19   $664.20   $664.20