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 $235.58   13.417%   $267.1878   $267.19   $267.20   $267.20  
  Purchase #2 $97.95   4.494%   $102.3519   $102.35   $102.35   $102.40  
  Purchase #3 $96.67   8.275%   $104.6694   $104.67   $104.65   $104.70  
  Purchase #4 $226.42   12.528%   $254.7859   $254.79   $254.80   $254.80  
  Purchase #5 $127.75   8.690%   $138.8515   $138.85   $138.85   $138.90  
  Purchase #6 $63.63   13.133%   $71.9865   $71.99   $72.00   $72.00  
  Purchase #7 $161.74   3.358%   $167.1712   $167.17   $167.15   $167.20  
  7 purchase totals = $1,009.74       $1,107.0042   $1,107.01   $1,107.00   $1,107.20