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 $211.48   12.467%   $237.8452   $237.85   $237.85   $237.80  
  Purchase #2 $23.97   6.853%   $25.6127   $25.61   $25.60   $25.60  
  Purchase #3 $82.74   10.168%   $91.153   $91.15   $91.15   $91.20  
  Purchase #4 $246.59   8.316%   $267.0964   $267.10   $267.10   $267.10  
  Purchase #5 $127.26   5.240%   $133.9284   $133.93   $133.95   $133.90  
  Purchase #6 $138.57   4.761%   $145.1673   $145.17   $145.15   $145.20  
  Purchase #7 $96.33   3.734%   $99.927   $99.93   $99.95   $99.90  
  7 purchase totals = $926.94       $1,000.7300   $1,000.74   $1,000.75   $1,000.70