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 $223.53   13.498%   $253.7021   $253.70   $253.70   $253.70  
  Purchase #2 $201.69   9.493%   $220.8364   $220.84   $220.85   $220.80  
  Purchase #3 $167.69   5.200%   $176.4099   $176.41   $176.40   $176.40  
  Purchase #4 $60.81   12.305%   $68.2927   $68.29   $68.30   $68.30  
  Purchase #5 $178.27   3.835%   $185.1067   $185.11   $185.10   $185.10  
  Purchase #6 $233.87   3.496%   $242.0461   $242.05   $242.05   $242.00  
  Purchase #7 $175.35   6.140%   $186.1165   $186.12   $186.10   $186.10  
  7 purchase totals = $1,241.21       $1,332.5104   $1,332.52   $1,332.50   $1,332.40