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 $191.76   3.753%   $198.9568   $198.96   $198.95   $199.00  
  Purchase #2 $44.60   4.605%   $46.6538   $46.65   $46.65   $46.70  
  Purchase #3 $56.86   7.762%   $61.2735   $61.27   $61.25   $61.30  
  Purchase #4 $167.52   9.596%   $183.5952   $183.60   $183.60   $183.60  
  Purchase #5 $133.77   9.830%   $146.9196   $146.92   $146.90   $146.90  
  Purchase #6 $178.35   7.510%   $191.7441   $191.74   $191.75   $191.70  
  Purchase #7 $207.57   7.515%   $223.1689   $223.17   $223.15   $223.20  
  7 purchase totals = $980.43       $1,052.3119   $1,052.31   $1,052.25   $1,052.40