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 $153.28   5.620%   $161.8943   $161.89   $161.90   $161.90  
  Purchase #2 $176.87   13.560%   $200.8536   $200.85   $200.85   $200.90  
  Purchase #3 $25.76   7.322%   $27.6461   $27.65   $27.65   $27.60  
  Purchase #4 $198.37   6.661%   $211.5834   $211.58   $211.60   $211.60  
  Purchase #5 $97.45   5.250%   $102.5661   $102.57   $102.55   $102.60  
  Purchase #6 $173.94   4.471%   $181.7169   $181.72   $181.70   $181.70  
  Purchase #7 $127.90   6.225%   $135.8618   $135.86   $135.85   $135.90  
  7 purchase totals = $953.57       $1,022.1222   $1,022.12   $1,022.10   $1,022.20