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 $32.94   9.277%   $35.9958   $36.00   $36.00   $36.00  
  Purchase #2 $87.64   5.407%   $92.3787   $92.38   $92.40   $92.40  
  Purchase #3 $119.41   12.510%   $134.3482   $134.35   $134.35   $134.30  
  Purchase #4 $167.53   3.126%   $172.767   $172.77   $172.75   $172.80  
  Purchase #5 $243.52   9.824%   $267.4434   $267.44   $267.45   $267.40  
  Purchase #6 $83.51   13.779%   $95.0168   $95.02   $95.00   $95.00  
  Purchase #7 $223.51   7.846%   $241.0466   $241.05   $241.05   $241.00  
  7 purchase totals = $958.06       $1,038.9965   $1,039.01   $1,039.00   $1,038.90