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 $231.98   13.144%   $262.4715   $262.47   $262.45   $262.50  
  Purchase #2 $232.95   3.322%   $240.6886   $240.69   $240.70   $240.70  
  Purchase #3 $221.41   3.301%   $228.7187   $228.72   $228.70   $228.70  
  Purchase #4 $135.64   4.846%   $142.2131   $142.21   $142.20   $142.20  
  Purchase #5 $97.35   5.277%   $102.4872   $102.49   $102.50   $102.50  
  Purchase #6 $92.59   4.481%   $96.739   $96.74   $96.75   $96.70  
  Purchase #7 $159.39   13.855%   $181.4735   $181.47   $181.45   $181.50  
  7 purchase totals = $1,171.31       $1,254.7916   $1,254.79   $1,254.75   $1,254.80