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 $52.30   7.544%   $56.2455   $56.25   $56.25   $56.20  
  Purchase #2 $199.35   8.453%   $216.2011   $216.20   $216.20   $216.20  
  Purchase #3 $160.66   5.709%   $169.8321   $169.83   $169.85   $169.80  
  Purchase #4 $137.55   7.204%   $147.4591   $147.46   $147.45   $147.50  
  Purchase #5 $240.51   6.577%   $256.3283   $256.33   $256.35   $256.30  
  Purchase #6 $167.40   12.601%   $188.4941   $188.49   $188.50   $188.50  
  Purchase #7 $223.41   5.203%   $235.034   $235.03   $235.05   $235.00  
  7 purchase totals = $1,181.18       $1,269.5942   $1,269.59   $1,269.65   $1,269.50