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 $247.33   7.532%   $265.9589   $265.96   $265.95   $266.00  
  Purchase #2 $162.91   6.532%   $173.5513   $173.55   $173.55   $173.60  
  Purchase #3 $21.29   5.841%   $22.5335   $22.53   $22.55   $22.50  
  Purchase #4 $7.92   6.499%   $8.4347   $8.43   $8.45   $8.40  
  Purchase #5 $158.51   8.220%   $171.5395   $171.54   $171.55   $171.50  
  Purchase #6 $126.27   6.532%   $134.518   $134.52   $134.50   $134.50  
  Purchase #7 $106.98   12.461%   $120.3108   $120.31   $120.30   $120.30  
  7 purchase totals = $831.21       $896.8467   $896.84   $896.85   $896.80