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 $148.49   12.568%   $167.1522   $167.15   $167.15   $167.20  
  Purchase #2 $246.36   8.868%   $268.2072   $268.21   $268.20   $268.20  
  Purchase #3 $163.40   12.444%   $183.7335   $183.73   $183.75   $183.70  
  Purchase #4 $60.80   8.502%   $65.9692   $65.97   $65.95   $66.00  
  Purchase #5 $200.49   7.819%   $216.1663   $216.17   $216.15   $216.20  
  Purchase #6 $24.61   8.803%   $26.7764   $26.78   $26.80   $26.80  
  Purchase #7 $127.34   6.108%   $135.1179   $135.12   $135.10   $135.10  
  7 purchase totals = $971.49       $1,063.1227   $1,063.13   $1,063.10   $1,063.20