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 $67.39   9.505%   $73.7954   $73.80   $73.80   $73.80  
  Purchase #2 $142.65   6.330%   $151.6797   $151.68   $151.70   $151.70  
  Purchase #3 $228.38   6.634%   $243.5307   $243.53   $243.55   $243.50  
  Purchase #4 $218.40   11.143%   $242.7363   $242.74   $242.75   $242.70  
  Purchase #5 $178.41   6.207%   $189.4839   $189.48   $189.50   $189.50  
  Purchase #6 $211.28   6.701%   $225.4379   $225.44   $225.45   $225.40  
  Purchase #7 $187.94   7.614%   $202.2498   $202.25   $202.25   $202.20  
  7 purchase totals = $1,234.45       $1,328.9137   $1,328.92   $1,329.00   $1,328.80