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 $238.43   9.399%   $260.84   $260.84   $260.85   $260.80  
  Purchase #2 $58.99   9.553%   $64.6253   $64.63   $64.65   $64.60  
  Purchase #3 $172.36   7.499%   $185.2853   $185.29   $185.30   $185.30  
  Purchase #4 $64.96   10.670%   $71.8912   $71.89   $71.90   $71.90  
  Purchase #5 $155.45   6.790%   $166.0051   $166.01   $166.00   $166.00  
  Purchase #6 $43.84   10.148%   $48.2889   $48.29   $48.30   $48.30  
  Purchase #7 $210.81   8.718%   $229.1884   $229.19   $229.20   $229.20  
  7 purchase totals = $944.84       $1,026.1242   $1,026.14   $1,026.20   $1,026.10