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 $181.71   12.556%   $204.5255   $204.53   $204.55   $204.50  
  Purchase #2 $214.72   6.279%   $228.2023   $228.20   $228.20   $228.20  
  Purchase #3 $218.70   13.330%   $247.8527   $247.85   $247.85   $247.90  
  Purchase #4 $219.38   7.356%   $235.5176   $235.52   $235.50   $235.50  
  Purchase #5 $177.62   9.109%   $193.7994   $193.80   $193.80   $193.80  
  Purchase #6 $32.32   12.333%   $36.306   $36.31   $36.30   $36.30  
  Purchase #7 $45.39   8.518%   $49.2563   $49.26   $49.25   $49.30  
  7 purchase totals = $1,089.84       $1,195.4598   $1,195.47   $1,195.45   $1,195.50