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 $58.86   10.419%   $64.9926   $64.99   $65.00   $65.00  
  Purchase #2 $118.65   12.359%   $133.314   $133.31   $133.30   $133.30  
  Purchase #3 $142.35   7.109%   $152.4697   $152.47   $152.45   $152.50  
  Purchase #4 $89.33   4.519%   $93.3668   $93.37   $93.35   $93.40  
  Purchase #5 $230.39   13.130%   $260.6402   $260.64   $260.65   $260.60  
  Purchase #6 $72.36   9.594%   $79.3022   $79.30   $79.30   $79.30  
  Purchase #7 $145.56   13.109%   $164.6415   $164.64   $164.65   $164.60  
  7 purchase totals = $857.50       $948.7270   $948.72   $948.70   $948.70