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 $194.39   6.403%   $206.8368   $206.84   $206.85   $206.80  
  Purchase #2 $243.53   12.229%   $273.3113   $273.31   $273.30   $273.30  
  Purchase #3 $232.87   8.507%   $252.6803   $252.68   $252.70   $252.70  
  Purchase #4 $18.95   5.110%   $19.9183   $19.92   $19.90   $19.90  
  Purchase #5 $205.49   8.199%   $222.3381   $222.34   $222.35   $222.30  
  Purchase #6 $175.25   13.234%   $198.4426   $198.44   $198.45   $198.40  
  Purchase #7 $55.37   9.559%   $60.6628   $60.66   $60.65   $60.70  
  7 purchase totals = $1,125.85       $1,234.1902   $1,234.19   $1,234.20   $1,234.10