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 $141.52   9.252%   $154.6134   $154.61   $154.60   $154.60  
  Purchase #2 $90.96   6.666%   $97.0234   $97.02   $97.00   $97.00  
  Purchase #3 $203.79   6.740%   $217.5254   $217.53   $217.55   $217.50  
  Purchase #4 $202.46   4.452%   $211.4735   $211.47   $211.45   $211.50  
  Purchase #5 $161.64   8.579%   $175.5071   $175.51   $175.50   $175.50  
  Purchase #6 $21.46   9.604%   $23.521   $23.52   $23.50   $23.50  
  Purchase #7 $241.94   6.653%   $258.0363   $258.04   $258.05   $258.00  
  7 purchase totals = $1,063.77       $1,137.7001   $1,137.70   $1,137.65   $1,137.60