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 $109.38   8.842%   $119.0514   $119.05   $119.05   $119.10  
  Purchase #2 $223.87   5.271%   $235.6702   $235.67   $235.65   $235.70  
  Purchase #3 $62.98   7.415%   $67.65   $67.65   $67.65   $67.70  
  Purchase #4 $214.85   13.512%   $243.8805   $243.88   $243.90   $243.90  
  Purchase #5 $137.27   4.582%   $143.5597   $143.56   $143.55   $143.60  
  Purchase #6 $138.79   8.333%   $150.3554   $150.36   $150.35   $150.40  
  Purchase #7 $10.69   4.695%   $11.1919   $11.19   $11.20   $11.20  
  7 purchase totals = $897.83       $971.3591   $971.36   $971.35   $971.60