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 $111.38   5.803%   $117.8434   $117.84   $117.85   $117.80  
  Purchase #2 $193.57   8.240%   $209.5202   $209.52   $209.50   $209.50  
  Purchase #3 $226.36   5.513%   $238.8392   $238.84   $238.85   $238.80  
  Purchase #4 $93.73   6.778%   $100.083   $100.08   $100.10   $100.10  
  Purchase #5 $35.66   8.180%   $38.577   $38.58   $38.60   $38.60  
  Purchase #6 $221.54   5.787%   $234.3605   $234.36   $234.35   $234.40  
  Purchase #7 $197.60   9.463%   $216.2989   $216.30   $216.30   $216.30  
  7 purchase totals = $1,079.84       $1,155.5222   $1,155.52   $1,155.55   $1,155.50