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 $118.87   12.506%   $133.7359   $133.74   $133.75   $133.70  
  Purchase #2 $5.59   10.735%   $6.1901   $6.19   $6.20   $6.20  
  Purchase #3 $151.27   4.410%   $157.941   $157.94   $157.95   $157.90  
  Purchase #4 $223.93   9.217%   $244.5696   $244.57   $244.55   $244.60  
  Purchase #5 $201.72   5.379%   $212.5705   $212.57   $212.55   $212.60  
  Purchase #6 $142.90   5.621%   $150.9324   $150.93   $150.95   $150.90  
  Purchase #7 $131.54   10.668%   $145.5727   $145.57   $145.55   $145.60  
  7 purchase totals = $975.82       $1,051.5122   $1,051.51   $1,051.50   $1,051.50