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 $61.62   8.217%   $66.6833   $66.68   $66.70   $66.70  
  Purchase #2 $225.85   13.292%   $255.87   $255.87   $255.85   $255.90  
  Purchase #3 $90.94   12.302%   $102.1274   $102.13   $102.15   $102.10  
  Purchase #4 $166.64   4.726%   $174.5154   $174.52   $174.50   $174.50  
  Purchase #5 $29.80   5.571%   $31.4602   $31.46   $31.45   $31.50  
  Purchase #6 $224.74   7.398%   $241.3663   $241.37   $241.35   $241.40  
  Purchase #7 $237.31   7.113%   $254.1899   $254.19   $254.20   $254.20  
  7 purchase totals = $1,036.90       $1,126.2125   $1,126.22   $1,126.20   $1,126.30