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 $212.93   10.251%   $234.7575   $234.76   $234.75   $234.80  
  Purchase #2 $173.93   13.640%   $197.6541   $197.65   $197.65   $197.70  
  Purchase #3 $98.37   6.106%   $104.3765   $104.38   $104.40   $104.40  
  Purchase #4 $219.87   11.625%   $245.4299   $245.43   $245.45   $245.40  
  Purchase #5 $88.45   8.764%   $96.2018   $96.20   $96.20   $96.20  
  Purchase #6 $189.25   8.163%   $204.6985   $204.70   $204.70   $204.70  
  Purchase #7 $71.64   5.124%   $75.3108   $75.31   $75.30   $75.30  
  7 purchase totals = $1,054.44       $1,158.4291   $1,158.43   $1,158.45   $1,158.50