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 $211.34   3.413%   $218.553   $218.55   $218.55   $218.60  
  Purchase #2 $218.35   6.220%   $231.9314   $231.93   $231.95   $231.90  
  Purchase #3 $60.52   7.790%   $65.2345   $65.23   $65.25   $65.20  
  Purchase #4 $137.31   7.762%   $147.968   $147.97   $147.95   $148.00  
  Purchase #5 $111.84   5.368%   $117.8436   $117.84   $117.85   $117.80  
  Purchase #6 $167.26   10.137%   $184.2151   $184.22   $184.20   $184.20  
  Purchase #7 $95.50   3.868%   $99.1939   $99.19   $99.20   $99.20  
  7 purchase totals = $1,002.12       $1,064.9395   $1,064.93   $1,064.95   $1,064.90