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 $86.56   10.120%   $95.3199   $95.32   $95.30   $95.30  
  Purchase #2 $212.78   10.598%   $235.3304   $235.33   $235.35   $235.30  
  Purchase #3 $87.26   8.148%   $94.3699   $94.37   $94.35   $94.40  
  Purchase #4 $220.84   7.811%   $238.0898   $238.09   $238.10   $238.10  
  Purchase #5 $88.93   10.519%   $98.2845   $98.28   $98.30   $98.30  
  Purchase #6 $135.76   9.310%   $148.3993   $148.40   $148.40   $148.40  
  Purchase #7 $109.64   10.712%   $121.3846   $121.38   $121.40   $121.40  
  7 purchase totals = $941.77       $1,031.1784   $1,031.17   $1,031.20   $1,031.20