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 $188.58   8.157%   $203.9625   $203.96   $203.95   $204.00  
  Purchase #2 $53.89   7.486%   $57.9242   $57.92   $57.90   $57.90  
  Purchase #3 $125.75   6.437%   $133.8445   $133.84   $133.85   $133.80  
  Purchase #4 $178.28   12.735%   $200.984   $200.98   $201.00   $201.00  
  Purchase #5 $64.65   10.702%   $71.5688   $71.57   $71.55   $71.60  
  Purchase #6 $162.43   12.842%   $183.2893   $183.29   $183.30   $183.30  
  Purchase #7 $118.28   5.210%   $124.4424   $124.44   $124.45   $124.40  
  7 purchase totals = $891.86       $976.0157   $976.00   $976.00   $976.00