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 $192.44   5.349%   $202.7336   $202.73   $202.75   $202.70  
  Purchase #2 $116.75   8.469%   $126.6376   $126.64   $126.65   $126.60  
  Purchase #3 $238.53   5.764%   $252.2789   $252.28   $252.30   $252.30  
  Purchase #4 $185.70   9.318%   $203.0035   $203.00   $203.00   $203.00  
  Purchase #5 $55.39   6.283%   $58.8702   $58.87   $58.85   $58.90  
  Purchase #6 $168.33   11.453%   $187.6088   $187.61   $187.60   $187.60  
  Purchase #7 $11.74   12.433%   $13.1996   $13.20   $13.20   $13.20  
  7 purchase totals = $968.88       $1,044.3322   $1,044.33   $1,044.35   $1,044.30