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 $214.79   9.287%   $234.7375   $234.74   $234.75   $234.70  
  Purchase #2 $52.56   6.249%   $55.8445   $55.84   $55.85   $55.80  
  Purchase #3 $184.83   10.394%   $204.0412   $204.04   $204.05   $204.00  
  Purchase #4 $163.79   5.604%   $172.9688   $172.97   $172.95   $173.00  
  Purchase #5 $62.53   9.479%   $68.4572   $68.46   $68.45   $68.50  
  Purchase #6 $188.82   9.442%   $206.6484   $206.65   $206.65   $206.60  
  Purchase #7 $35.68   5.802%   $37.7502   $37.75   $37.75   $37.80  
  7 purchase totals = $903.00       $980.4478   $980.45   $980.45   $980.40