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 $143.40   12.478%   $161.2935   $161.29   $161.30   $161.30  
  Purchase #2 $93.91   13.443%   $106.5343   $106.53   $106.55   $106.50  
  Purchase #3 $113.95   5.567%   $120.2936   $120.29   $120.30   $120.30  
  Purchase #4 $58.67   6.486%   $62.4753   $62.48   $62.50   $62.50  
  Purchase #5 $97.98   9.666%   $107.4507   $107.45   $107.45   $107.50  
  Purchase #6 $227.74   13.128%   $257.6377   $257.64   $257.65   $257.60  
  Purchase #7 $197.46   4.842%   $207.021   $207.02   $207.00   $207.00  
  7 purchase totals = $933.11       $1,022.7061   $1,022.70   $1,022.75   $1,022.70