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 $212.97   5.102%   $223.8357   $223.84   $223.85   $223.80  
  Purchase #2 $204.66   10.108%   $225.347   $225.35   $225.35   $225.30  
  Purchase #3 $158.32   5.600%   $167.1859   $167.19   $167.20   $167.20  
  Purchase #4 $58.29   10.529%   $64.4274   $64.43   $64.45   $64.40  
  Purchase #5 $240.53   9.285%   $262.8632   $262.86   $262.85   $262.90  
  Purchase #6 $58.99   8.829%   $64.1982   $64.20   $64.20   $64.20  
  Purchase #7 $40.25   10.657%   $44.5394   $44.54   $44.55   $44.50  
  7 purchase totals = $974.01       $1,052.3968   $1,052.41   $1,052.45   $1,052.30