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 $241.59   12.595%   $272.0183   $272.02   $272.00   $272.00  
  Purchase #2 $140.79   8.207%   $152.3446   $152.34   $152.35   $152.30  
  Purchase #3 $91.43   12.544%   $102.899   $102.90   $102.90   $102.90  
  Purchase #4 $72.58   9.755%   $79.6602   $79.66   $79.65   $79.70  
  Purchase #5 $161.91   7.687%   $174.356   $174.36   $174.35   $174.40  
  Purchase #6 $230.40   4.437%   $240.6228   $240.62   $240.60   $240.60  
  Purchase #7 $37.96   3.373%   $39.2404   $39.24   $39.25   $39.20  
  7 purchase totals = $976.66       $1,061.1413   $1,061.14   $1,061.10   $1,061.10