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 $65.79   8.456%   $71.3532   $71.35   $71.35   $71.40  
  Purchase #2 $219.92   12.425%   $247.2451   $247.25   $247.25   $247.20  
  Purchase #3 $191.59   3.851%   $198.9681   $198.97   $198.95   $199.00  
  Purchase #4 $150.57   12.272%   $169.048   $169.05   $169.05   $169.00  
  Purchase #5 $209.91   5.531%   $221.5201   $221.52   $221.50   $221.50  
  Purchase #6 $199.44   13.400%   $226.165   $226.17   $226.15   $226.20  
  Purchase #7 $192.56   12.506%   $216.6416   $216.64   $216.65   $216.60  
  7 purchase totals = $1,229.78       $1,350.9411   $1,350.95   $1,350.90   $1,350.90