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 $148.68   11.473%   $165.7381   $165.74   $165.75   $165.70  
  Purchase #2 $184.95   12.457%   $207.9892   $207.99   $208.00   $208.00  
  Purchase #3 $220.74   10.178%   $243.2069   $243.21   $243.20   $243.20  
  Purchase #4 $95.52   5.497%   $100.7707   $100.77   $100.75   $100.80  
  Purchase #5 $31.69   3.833%   $32.9047   $32.90   $32.90   $32.90  
  Purchase #6 $27.94   3.449%   $28.9037   $28.90   $28.90   $28.90  
  Purchase #7 $233.59   4.372%   $243.8026   $243.80   $243.80   $243.80  
  7 purchase totals = $943.11       $1,023.3159   $1,023.31   $1,023.30   $1,023.30