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 $184.42   10.103%   $203.052   $203.05   $203.05   $203.10  
  Purchase #2 $120.94   13.557%   $137.3358   $137.34   $137.35   $137.30  
  Purchase #3 $112.82   4.580%   $117.9872   $117.99   $118.00   $118.00  
  Purchase #4 $236.70   4.176%   $246.5846   $246.58   $246.60   $246.60  
  Purchase #5 $100.65   5.384%   $106.069   $106.07   $106.05   $106.10  
  Purchase #6 $71.65   8.160%   $77.4966   $77.50   $77.50   $77.50  
  Purchase #7 $229.40   13.117%   $259.4904   $259.49   $259.50   $259.50  
  7 purchase totals = $1,056.58       $1,148.0156   $1,148.02   $1,148.05   $1,148.10