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 $178.93   4.797%   $187.5133   $187.51   $187.50   $187.50  
  Purchase #2 $184.82   8.852%   $201.1803   $201.18   $201.20   $201.20  
  Purchase #3 $195.46   9.279%   $213.5967   $213.60   $213.60   $213.60  
  Purchase #4 $71.68   4.702%   $75.0504   $75.05   $75.05   $75.10  
  Purchase #5 $205.37   11.278%   $228.5316   $228.53   $228.55   $228.50  
  Purchase #6 $58.52   10.200%   $64.489   $64.49   $64.50   $64.50  
  Purchase #7 $53.97   3.480%   $55.8482   $55.85   $55.85   $55.80  
  7 purchase totals = $948.75       $1,026.2095   $1,026.21   $1,026.25   $1,026.20