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 $186.82   7.828%   $201.4443   $201.44   $201.45   $201.40  
  Purchase #2 $22.29   13.268%   $25.2474   $25.25   $25.25   $25.20  
  Purchase #3 $228.67   8.268%   $247.5764   $247.58   $247.60   $247.60  
  Purchase #4 $155.30   7.633%   $167.154   $167.15   $167.15   $167.20  
  Purchase #5 $195.29   7.797%   $210.5168   $210.52   $210.50   $210.50  
  Purchase #6 $166.56   10.601%   $184.217   $184.22   $184.20   $184.20  
  Purchase #7 $38.34   12.694%   $43.2069   $43.21   $43.20   $43.20  
  7 purchase totals = $993.27       $1,079.3628   $1,079.37   $1,079.35   $1,079.30