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 $54.91   10.809%   $60.8452   $60.85   $60.85   $60.80  
  Purchase #2 $187.37   5.522%   $197.7166   $197.72   $197.70   $197.70  
  Purchase #3 $220.43   6.172%   $234.0349   $234.03   $234.05   $234.00  
  Purchase #4 $216.51   8.682%   $235.3074   $235.31   $235.30   $235.30  
  Purchase #5 $80.92   4.339%   $84.4311   $84.43   $84.45   $84.40  
  Purchase #6 $88.95   7.514%   $95.6337   $95.63   $95.65   $95.60  
  Purchase #7 $118.76   6.477%   $126.4521   $126.45   $126.45   $126.50  
  7 purchase totals = $967.85       $1,034.4210   $1,034.42   $1,034.45   $1,034.30