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 $231.92   5.404%   $244.453   $244.45   $244.45   $244.50  
  Purchase #2 $66.51   5.743%   $70.3297   $70.33   $70.35   $70.30  
  Purchase #3 $12.39   3.568%   $12.8321   $12.83   $12.85   $12.80  
  Purchase #4 $191.57   8.498%   $207.8496   $207.85   $207.85   $207.80  
  Purchase #5 $29.32   11.440%   $32.6742   $32.67   $32.65   $32.70  
  Purchase #6 $205.31   3.151%   $211.7793   $211.78   $211.80   $211.80  
  Purchase #7 $145.58   6.301%   $154.753   $154.75   $154.75   $154.80  
  7 purchase totals = $882.60       $934.6709   $934.66   $934.70   $934.70