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 $188.59   8.325%   $204.2901   $204.29   $204.30   $204.30  
  Purchase #2 $247.51   4.768%   $259.3113   $259.31   $259.30   $259.30  
  Purchase #3 $213.52   3.211%   $220.3761   $220.38   $220.40   $220.40  
  Purchase #4 $183.51   9.854%   $201.5931   $201.59   $201.60   $201.60  
  Purchase #5 $106.41   12.321%   $119.5208   $119.52   $119.50   $119.50  
  Purchase #6 $228.94   11.783%   $255.916   $255.92   $255.90   $255.90  
  Purchase #7 $38.95   12.432%   $43.7923   $43.79   $43.80   $43.80  
  7 purchase totals = $1,207.43       $1,304.7997   $1,304.80   $1,304.80   $1,304.80