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 $226.96   9.164%   $247.7586   $247.76   $247.75   $247.80  
  Purchase #2 $85.97   8.473%   $93.2542   $93.25   $93.25   $93.30  
  Purchase #3 $225.44   9.821%   $247.5805   $247.58   $247.60   $247.60  
  Purchase #4 $90.77   13.623%   $103.1356   $103.14   $103.15   $103.10  
  Purchase #5 $147.88   8.224%   $160.0417   $160.04   $160.05   $160.00  
  Purchase #6 $193.38   6.343%   $205.6461   $205.65   $205.65   $205.60  
  Purchase #7 $89.98   13.794%   $102.3918   $102.39   $102.40   $102.40  
  7 purchase totals = $1,060.38       $1,159.8085   $1,159.81   $1,159.85   $1,159.80