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 $217.99   12.269%   $244.7352   $244.74   $244.75   $244.70  
  Purchase #2 $164.96   11.322%   $183.6368   $183.64   $183.65   $183.60  
  Purchase #3 $114.68   12.348%   $128.8407   $128.84   $128.85   $128.80  
  Purchase #4 $23.40   3.430%   $24.2026   $24.20   $24.20   $24.20  
  Purchase #5 $83.69   4.707%   $87.6293   $87.63   $87.65   $87.60  
  Purchase #6 $134.71   11.625%   $150.37   $150.37   $150.35   $150.40  
  Purchase #7 $189.56   6.205%   $201.3222   $201.32   $201.30   $201.30  
  7 purchase totals = $928.99       $1,020.7368   $1,020.74   $1,020.75   $1,020.60