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 $204.62   12.702%   $230.6108   $230.61   $230.60   $230.60  
  Purchase #2 $220.79   10.348%   $243.6373   $243.64   $243.65   $243.60  
  Purchase #3 $122.25   9.492%   $133.854   $133.85   $133.85   $133.90  
  Purchase #4 $142.57   11.754%   $159.3277   $159.33   $159.35   $159.30  
  Purchase #5 $75.66   7.646%   $81.445   $81.45   $81.45   $81.40  
  Purchase #6 $75.66   5.576%   $79.8788   $79.88   $79.90   $79.90  
  Purchase #7 $232.97   3.315%   $240.693   $240.69   $240.70   $240.70  
  7 purchase totals = $1,074.52       $1,169.4466   $1,169.45   $1,169.50   $1,169.40