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 $233.33   13.628%   $265.1282   $265.13   $265.15   $265.10  
  Purchase #2 $61.66   6.527%   $65.6845   $65.68   $65.70   $65.70  
  Purchase #3 $27.30   9.213%   $29.8151   $29.82   $29.80   $29.80  
  Purchase #4 $219.61   11.194%   $244.1931   $244.19   $244.20   $244.20  
  Purchase #5 $11.61   11.716%   $12.9702   $12.97   $12.95   $13.00  
  Purchase #6 $152.88   4.349%   $159.5288   $159.53   $159.55   $159.50  
  Purchase #7 $147.76   12.354%   $166.0143   $166.01   $166.00   $166.00  
  7 purchase totals = $854.15       $943.3342   $943.33   $943.35   $943.30