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 $47.81   11.180%   $53.1552   $53.16   $53.15   $53.20  
  Purchase #2 $65.25   5.759%   $69.0077   $69.01   $69.00   $69.00  
  Purchase #3 $57.77   12.301%   $64.8763   $64.88   $64.90   $64.90  
  Purchase #4 $169.52   3.561%   $175.5566   $175.56   $175.55   $175.60  
  Purchase #5 $128.29   6.657%   $136.8303   $136.83   $136.85   $136.80  
  Purchase #6 $53.73   11.861%   $60.1029   $60.10   $60.10   $60.10  
  Purchase #7 $175.81   9.200%   $191.9845   $191.98   $192.00   $192.00  
  7 purchase totals = $698.18       $751.5135   $751.52   $751.55   $751.60