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 $243.49   11.421%   $271.299   $271.30   $271.30   $271.30  
  Purchase #2 $145.33   8.330%   $157.436   $157.44   $157.45   $157.40  
  Purchase #3 $191.37   11.607%   $213.5823   $213.58   $213.60   $213.60  
  Purchase #4 $165.81   11.228%   $184.4271   $184.43   $184.45   $184.40  
  Purchase #5 $239.32   7.435%   $257.1134   $257.11   $257.10   $257.10  
  Purchase #6 $127.52   3.192%   $131.5904   $131.59   $131.60   $131.60  
  Purchase #7 $29.60   7.871%   $31.9298   $31.93   $31.95   $31.90  
  7 purchase totals = $1,142.44       $1,247.3780   $1,247.38   $1,247.45   $1,247.30