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 $199.52   6.213%   $211.9162   $211.92   $211.90   $211.90  
  Purchase #2 $127.98   11.171%   $142.2766   $142.28   $142.30   $142.30  
  Purchase #3 $212.43   5.343%   $223.7801   $223.78   $223.80   $223.80  
  Purchase #4 $201.80   5.733%   $213.3692   $213.37   $213.35   $213.40  
  Purchase #5 $232.89   13.170%   $263.5616   $263.56   $263.55   $263.60  
  Purchase #6 $71.81   7.217%   $76.9925   $76.99   $77.00   $77.00  
  Purchase #7 $221.54   9.251%   $242.0347   $242.03   $242.05   $242.00  
  7 purchase totals = $1,267.97       $1,373.9309   $1,373.93   $1,373.95   $1,374.00