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 $250.57   13.298%   $283.8908   $283.89   $283.90   $283.90  
  Purchase #2 $117.26   7.655%   $126.2363   $126.24   $126.25   $126.20  
  Purchase #3 $94.26   8.373%   $102.1524   $102.15   $102.15   $102.20  
  Purchase #4 $81.37   3.653%   $84.3424   $84.34   $84.35   $84.30  
  Purchase #5 $118.92   11.651%   $132.7754   $132.78   $132.80   $132.80  
  Purchase #6 $173.88   3.108%   $179.2842   $179.28   $179.30   $179.30  
  Purchase #7 $150.42   6.660%   $160.438   $160.44   $160.45   $160.40  
  7 purchase totals = $986.68       $1,069.1195   $1,069.12   $1,069.20   $1,069.10