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 $204.91   4.474%   $214.0777   $214.08   $214.10   $214.10  
  Purchase #2 $166.93   13.148%   $188.878   $188.88   $188.90   $188.90  
  Purchase #3 $211.54   7.473%   $227.3484   $227.35   $227.35   $227.30  
  Purchase #4 $191.34   6.432%   $203.647   $203.65   $203.65   $203.60  
  Purchase #5 $229.96   9.376%   $251.521   $251.52   $251.50   $251.50  
  Purchase #6 $161.51   13.699%   $183.6353   $183.64   $183.65   $183.60  
  Purchase #7 $51.85   13.160%   $58.6735   $58.67   $58.65   $58.70  
  7 purchase totals = $1,218.04       $1,327.7809   $1,327.79   $1,327.80   $1,327.70