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 $210.32   11.495%   $234.4963   $234.50   $234.50   $234.50  
  Purchase #2 $127.94   5.399%   $134.8475   $134.85   $134.85   $134.80  
  Purchase #3 $170.48   4.474%   $178.1073   $178.11   $178.10   $178.10  
  Purchase #4 $193.94   4.490%   $202.6479   $202.65   $202.65   $202.60  
  Purchase #5 $107.84   9.725%   $118.3274   $118.33   $118.35   $118.30  
  Purchase #6 $153.85   5.154%   $161.7794   $161.78   $161.80   $161.80  
  Purchase #7 $41.40   7.652%   $44.5679   $44.57   $44.55   $44.60  
  7 purchase totals = $1,005.77       $1,074.7737   $1,074.79   $1,074.80   $1,074.70