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 $39.78   10.203%   $43.8388   $43.84   $43.85   $43.80  
  Purchase #2 $93.68   11.309%   $104.2743   $104.27   $104.25   $104.30  
  Purchase #3 $203.70   13.164%   $230.5151   $230.52   $230.50   $230.50  
  Purchase #4 $52.82   8.483%   $57.3007   $57.30   $57.30   $57.30  
  Purchase #5 $147.65   9.403%   $161.5335   $161.53   $161.55   $161.50  
  Purchase #6 $63.99   7.758%   $68.9543   $68.95   $68.95   $69.00  
  Purchase #7 $121.64   9.738%   $133.4853   $133.49   $133.50   $133.50  
  7 purchase totals = $723.26       $799.9020   $799.90   $799.90   $799.90