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 $196.56   3.811%   $204.0509   $204.05   $204.05   $204.10  
  Purchase #2 $25.73   12.415%   $28.9244   $28.92   $28.90   $28.90  
  Purchase #3 $206.93   9.213%   $225.9945   $225.99   $226.00   $226.00  
  Purchase #4 $10.58   3.518%   $10.9522   $10.95   $10.95   $11.00  
  Purchase #5 $170.67   7.846%   $184.0608   $184.06   $184.05   $184.10  
  Purchase #6 $165.25   9.701%   $181.2809   $181.28   $181.30   $181.30  
  Purchase #7 $214.43   6.606%   $228.5952   $228.60   $228.60   $228.60  
  7 purchase totals = $990.15       $1,063.8589   $1,063.85   $1,063.85   $1,064.00