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 $222.52   8.708%   $241.897   $241.90   $241.90   $241.90  
  Purchase #2 $87.38   3.449%   $90.3937   $90.39   $90.40   $90.40  
  Purchase #3 $78.92   7.655%   $84.9613   $84.96   $84.95   $85.00  
  Purchase #4 $143.95   13.526%   $163.4207   $163.42   $163.40   $163.40  
  Purchase #5 $136.25   4.711%   $142.6687   $142.67   $142.65   $142.70  
  Purchase #6 $212.86   6.332%   $226.3383   $226.34   $226.35   $226.30  
  Purchase #7 $58.31   8.370%   $63.1905   $63.19   $63.20   $63.20  
  7 purchase totals = $940.19       $1,012.8702   $1,012.87   $1,012.85   $1,012.90