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 $203.34   6.141%   $215.8271   $215.83   $215.85   $215.80  
  Purchase #2 $8.84   7.273%   $9.4829   $9.48   $9.50   $9.50  
  Purchase #3 $169.40   3.376%   $175.1189   $175.12   $175.10   $175.10  
  Purchase #4 $87.68   4.524%   $91.6466   $91.65   $91.65   $91.60  
  Purchase #5 $203.88   12.323%   $229.0041   $229.00   $229.00   $229.00  
  Purchase #6 $100.33   3.134%   $103.4743   $103.47   $103.45   $103.50  
  Purchase #7 $174.47   11.547%   $194.6161   $194.62   $194.60   $194.60  
  7 purchase totals = $947.94       $1,019.1700   $1,019.17   $1,019.15   $1,019.10