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 $176.30   4.697%   $184.5808   $184.58   $184.60   $184.60  
  Purchase #2 $172.84   3.351%   $178.6319   $178.63   $178.65   $178.60  
  Purchase #3 $63.70   5.312%   $67.0837   $67.08   $67.10   $67.10  
  Purchase #4 $118.56   12.122%   $132.9318   $132.93   $132.95   $132.90  
  Purchase #5 $213.41   5.392%   $224.9171   $224.92   $224.90   $224.90  
  Purchase #6 $179.48   12.282%   $201.5237   $201.52   $201.50   $201.50  
  Purchase #7 $194.46   8.289%   $210.5788   $210.58   $210.60   $210.60  
  7 purchase totals = $1,118.75       $1,200.2478   $1,200.24   $1,200.30   $1,200.20