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 $191.76   5.649%   $202.5925   $202.59   $202.60   $202.60  
  Purchase #2 $69.73   3.439%   $72.128   $72.13   $72.15   $72.10  
  Purchase #3 $234.36   12.702%   $264.1284   $264.13   $264.15   $264.10  
  Purchase #4 $17.39   11.714%   $19.4271   $19.43   $19.45   $19.40  
  Purchase #5 $189.57   7.182%   $203.1849   $203.18   $203.20   $203.20  
  Purchase #6 $88.41   5.309%   $93.1037   $93.10   $93.10   $93.10  
  Purchase #7 $203.96   4.344%   $212.82   $212.82   $212.80   $212.80  
  7 purchase totals = $995.18       $1,067.3846   $1,067.38   $1,067.45   $1,067.30