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 $246.29   3.147%   $254.0407   $254.04   $254.05   $254.00  
  Purchase #2 $212.54   9.826%   $233.4242   $233.42   $233.40   $233.40  
  Purchase #3 $22.70   13.849%   $25.8437   $25.84   $25.85   $25.80  
  Purchase #4 $43.52   3.426%   $45.011   $45.01   $45.00   $45.00  
  Purchase #5 $146.42   12.800%   $165.1618   $165.16   $165.15   $165.20  
  Purchase #6 $202.65   5.850%   $214.505   $214.51   $214.50   $214.50  
  Purchase #7 $207.84   3.135%   $214.3558   $214.36   $214.35   $214.40  
  7 purchase totals = $1,081.96       $1,152.3422   $1,152.34   $1,152.30   $1,152.30