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 $62.60   5.258%   $65.8915   $65.89   $65.90   $65.90  
  Purchase #2 $127.69   5.867%   $135.1816   $135.18   $135.20   $135.20  
  Purchase #3 $233.52   9.107%   $254.7867   $254.79   $254.80   $254.80  
  Purchase #4 $187.71   11.592%   $209.4693   $209.47   $209.45   $209.50  
  Purchase #5 $111.28   13.776%   $126.6099   $126.61   $126.60   $126.60  
  Purchase #6 $34.27   13.447%   $38.8783   $38.88   $38.90   $38.90  
  Purchase #7 $204.27   3.260%   $210.9292   $210.93   $210.95   $210.90  
  7 purchase totals = $961.34       $1,041.7465   $1,041.75   $1,041.80   $1,041.80