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 $247.36   7.644%   $266.2682   $266.27   $266.25   $266.30  
  Purchase #2 $161.28   6.179%   $171.2455   $171.25   $171.25   $171.20  
  Purchase #3 $25.50   6.415%   $27.1358   $27.14   $27.15   $27.10  
  Purchase #4 $168.50   3.562%   $174.502   $174.50   $174.50   $174.50  
  Purchase #5 $191.74   5.854%   $202.9645   $202.96   $202.95   $203.00  
  Purchase #6 $100.79   12.739%   $113.6296   $113.63   $113.65   $113.60  
  Purchase #7 $98.29   12.251%   $110.3315   $110.33   $110.35   $110.30  
  7 purchase totals = $993.46       $1,066.0771   $1,066.08   $1,066.10   $1,066.00