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 $49.28   5.196%   $51.8406   $51.84   $51.85   $51.80  
  Purchase #2 $208.73   10.571%   $230.7948   $230.79   $230.80   $230.80  
  Purchase #3 $31.58   5.476%   $33.3093   $33.31   $33.30   $33.30  
  Purchase #4 $77.60   10.203%   $85.5175   $85.52   $85.50   $85.50  
  Purchase #5 $196.83   6.631%   $209.8818   $209.88   $209.90   $209.90  
  Purchase #6 $113.54   6.570%   $120.9996   $121.00   $121.00   $121.00  
  Purchase #7 $84.80   11.202%   $94.2993   $94.30   $94.30   $94.30  
  7 purchase totals = $762.36       $826.6429   $826.64   $826.65   $826.60