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 $57.78   12.644%   $65.0857   $65.09   $65.10   $65.10  
  Purchase #2 $213.55   9.344%   $233.5041   $233.50   $233.50   $233.50  
  Purchase #3 $92.29   4.598%   $96.5335   $96.53   $96.55   $96.50  
  Purchase #4 $67.29   9.372%   $73.5964   $73.60   $73.60   $73.60  
  Purchase #5 $124.43   9.157%   $135.8241   $135.82   $135.80   $135.80  
  Purchase #6 $85.75   10.478%   $94.7349   $94.73   $94.75   $94.70  
  Purchase #7 $220.84   9.241%   $241.2478   $241.25   $241.25   $241.20  
  7 purchase totals = $861.93       $940.5265   $940.52   $940.55   $940.40