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 $229.34   5.374%   $241.6647   $241.66   $241.65   $241.70  
  Purchase #2 $67.93   9.717%   $74.5308   $74.53   $74.55   $74.50  
  Purchase #3 $162.90   8.593%   $176.898   $176.90   $176.90   $176.90  
  Purchase #4 $45.94   10.572%   $50.7968   $50.80   $50.80   $50.80  
  Purchase #5 $49.67   9.384%   $54.331   $54.33   $54.35   $54.30  
  Purchase #6 $213.25   8.841%   $232.1034   $232.10   $232.10   $232.10  
  Purchase #7 $223.30   6.481%   $237.7721   $237.77   $237.75   $237.80  
  7 purchase totals = $992.33       $1,068.0968   $1,068.09   $1,068.10   $1,068.10