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 $35.92   3.855%   $37.3047   $37.30   $37.30   $37.30  
  Purchase #2 $217.60   9.223%   $237.6692   $237.67   $237.65   $237.70  
  Purchase #3 $149.36   10.386%   $164.8725   $164.87   $164.85   $164.90  
  Purchase #4 $36.92   3.746%   $38.303   $38.30   $38.30   $38.30  
  Purchase #5 $215.40   9.137%   $235.0811   $235.08   $235.10   $235.10  
  Purchase #6 $160.52   5.305%   $169.0356   $169.04   $169.05   $169.00  
  Purchase #7 $178.68   8.672%   $194.1751   $194.18   $194.20   $194.20  
  7 purchase totals = $994.40       $1,076.4412   $1,076.44   $1,076.45   $1,076.50